The present invention relates to a pivot mechanism and in particular, but not exclusively, to a pivot mechanism for use in a seat recliner mechanism. The invention also relates to a recliner mechanism and a vehicle seat including such a mechanism.
Many vehicle seats include a tilting/tipping mechanism that allows the angle of the seat back to be adjusted The seat back is generally attached to the seat base through a pivot mechanism that includes a locking mechanism for locking the seat back at the desired angle.
In one such pivot mechanism, for example as described in DE-OS-293 1873, the seat back is attached to a pivot arm that is provided with a set of ratchet teeth. Those teeth are engaged by a locking plate having a complementary set of teeth. The locking plate can be moved away from the pivot arm to disengage the two sets of teeth, allowing the angle of the seat back to be adjusted, and can the be moved back towards the pivot arm, to engage the teeth and lock the seat back in position.
The pivot mechanism naturally has to be able to withstand a number of forces during normal use including in particular the rearward force caused by a passenger leaning against the seat back. However, for safety and to comply with worldwide legislation, it also has to be able to withstand the much greater forces that might be generated if the vehicle is involved in a collision. In particular, if the seat back carries the upper anchoring point for the seat belt, a very large forwards force may be generated in the event of a frontal collision, owing to the inertia of the passenger. Such transient forces may be many times greater than the forces experienced during normal usage and the pivot mechanism must be able to withstand them without collapsing.
The very large forces generated by a collision can cause plastic deformation of the pivot mechanism. For example, the pivot pin on which the pivot arm is mounted may be driven forwards, causing partial separation of the two sets of teeth forming the locking mechanism. The forces carried by the locking mechanism may then be concentrated on just one or two of the teeth, causing those teeth to fail, followed by sequential failure of all the remaining teeth as the load is transferred to them (the so-called xe2x80x9cdomino effectxe2x80x9d).
It is an object of the present invention to provide a pivot mechanism that mitigates at least some of the disadvantages of prior art pivot mechanisms.
According to one aspect of the present invention there is provided a pivot mechanism including a first element, a second element that is rotatably mounted on the first element via a pivot means, and a locking mechanism including a convex tooth segment provided on the second element and a locking member having a concave tooth segment, the locking member being mounted on the first element for movement between a locked position in which the convex and concave tooth segments are engaged preventing rotation of the second element and an unlocked position in which the tooth segments are disengaged; characterised in that the centre of curvature of the convex tooth segment is offset from the centre of curvature of the concave tooth segment whereby, in normal usage, the convex and concave tooth segments are only partially engaged when the locking member is in the locked position.
Owing to the offset of the centres of curvature, the mechanism is able to absorb some plastic deformation without failing. The deformation has the effect of driving more of the teeth into engagement, thereby spreading the load between the tooth segments and increasing the strength of the locking mechanism.
Advantageously, the point of engagement between the tooth segments is towards one end of the concave tooth segment, which in the case of a pivot mechanism for a vehicle seat is the rear end of the tooth segment. This gives the mechanism greater strength in one direction than the other, which is important in situations where the pivot mechanism is more likely to encounter very large loads in one direction than another, for example in a vehicle that is involved in a collision. In many countries, these load bearing characteristics are dictated by legislation. The off-centre location of the engagement point also serves to remove free play from the mechanism and compensates automatically for both tolerance and wear.
The degree and direction of offset depends on the design criteria including the balance of the strength requirements for loads acting in different directions on the mechanism, and the dimensions and load-bearing characteristics of the other components of the mechanism.
Advantageously, the effective radius of the concave tooth segment is larger than the effective radius of the convex tooth segment. The ratio of the effective radii may be in the range 1.0-1.3, preferably 1.1-1.2, more preferably approximately 1.15.
Advantageously, the centres of curvature of the convex and concave tooth segments are located on a line that is substantially radial to both tooth segments, and said line intersects the concave tooth segment towards one end thereof, which in the case of a pivot mechanism for a vehicle seat is the rear end of the tooth segment.
Advantageously, the pivot mechanism includes a cam element that engages the locking member and is constructed and arranged to control movement thereof been said locked and unlocked positions, said cam element including a first cam surface for driving the locking member towards the locked position and a second cam surface for driving the locking member towards the unlocked position.
According to a further aspect of the invention there is provided a pivot mechanism including a first element, a second element that is rotatably mounted on the first element via a pivot means, and a locking mechanism including a convex tooth segment provided on the second element, a locking member having a concave tooth segment, the locking member being mounted on the first element for movement between a locked position in which the convex and concave tooth segments are engaged preventing rotation of the second element and an unlocked position in which the tooth segments are disengaged, and a cam element that engages the locking member and is constructed and arranged to control movement thereof between said locked and unlocked positions; characterised in that the cam element includes a first cam surface for driving the locking member towards the locked position and a second cam surface for driving the locking member towards the unlocked position.
According to a further aspect of the invention there is provided a pivot mechanism including a first element, a second element that is rotatably mounted on the first element via a pivot means, a locking member having a first locking formation that complements a second locking formation provided on the second element, the locking member being mounted for movement between a locked position in which the first and second locking formations are engaged, so preventing rotation of the second element, and an unlocked position in which the locking formations are disengaged, at least one guide member for guiding movement of the locking member and a control member for controlling movement of the locking member; characterised in that when the locking member is in the locked position, the control member exerts on the locking member a force having a first component that acts in the direction of movement of the locking member and a second component acts perpendicular to said direction of movement.
When the mechanism is locked, the locking member is urged against the second element by the control member. The force acting upon the locking member has a first component that acts in the direction of movement of the locking member, which locks the second element in position, and a second component that is perpendicular to the direction of movement of the locking member, which urges the locking member against the guide member (or one of the guide members). This removes chuck (free play) from the mechanism and compensates for wear of the components.
Advantageously, the first and second locking formations engage one another at an engagement point P, which is offset from a line L that extends through the pivot axis of the pivot means in the direction of movement of the locking member.
Advantageously, the control member includes a rotatable cam and the first and second locking formations engage one another at an engagement point P, which is offset from a line that extends through the pivot axis of the pivot means and the rotation axis of the cam.
The pivot mechanism may have locking formations allowing the first and second elements to be locked in one or more positions.
According to a further aspect of the invention there is provided a pivot mechanism including a first element, a second element that is rotatably mounted on the first element via pivot means, a locking member having a first locking formation that complements a second locking formation provided on the second element, the locking member being mounted for movement between a locked position in which the first and second locking formations are engaged, so preventing rotation of the second element, and an unlocked position in which the locking formations are disengaged, at least one guide member for guiding movement of the locking member and a control member for controlling movement of the locking member; characterised by a compensating element that urges the locking member against said at least one guide member to remove chuck from the mechanism. The wedge member removes chuck (free play) from the mechanism and compensates for wear of the components.
Advantageously, the compensating element includes a wedge member that is urged into a gap adjacent the locking member. The wedge member may be urged into the gap by means of a spring.
According to a further aspect of the invention there is provided a recliner mechanism for a vehicle seat having a seat base and a reclining seat back, said recliner mechanism including a pivot mechanism as described in one of the preceding statements of invention.
The recliner mechanism may include a lock out mechanism for driving the locking member into engagement with the convex tooth segment in the event of a collision.
According to a further aspect of the invention there is provided a recliner mechanism for a vehicle seat having a seat base and a reclining seat back, said recliner mechanism including a pivot mechanism that includes a pivot arm rotatably mounted on a base member via a pivot pin, and a locking mechanism including a convex tooth segment provided on the pivot arm, and a locking member having a concave tooth segment, the locking member being mounted on the base member for movement between a locked position in which the convex and concave tooth segments are engaged preventing rotation of the pivot arm and an unlocked position in which the tooth segments are disengaged; characterised by a lock out mechanism for driving the locking member into engagement with the convex tooth segment in the event of a collision.
According to a further aspect of the invention there is provided a vehicle seat including a seat base and a reclining seat back that is attached to the seat base by means of a recliner mechanism according to the preceding statement of invention.